Plasmonic Nanostructures Could Change the Landscape of Optoelectronics

Research provides greater understanding of how plasmonics works for an entire device, potentially offering a simpler alternative

2 min read
Plasmonic Nanostructures Could Change the Landscape of Optoelectronics
Rice University researchers (clockwise from front) Man-Nung Su, Wei-Shun Chang and Fangfang Wen discovered a new method to tune the light-induced vibrations of nanoparticles through slight alterations to the surface to which they are attached.
Photo: Rice University

Scientists have high hopes that the emerging field of plasmonics can improve technologies such as photovoltaicsLEDs, and other optoelectronics. It’s a natural fit: Plasmonics exploits the oscillations in the density of electrons that are generated when photons hit a metal surface.

However, it’s been studied in a bit too much isolation. Scientists have only looked at the phenomenon in isloated metal nanostructures and not the metal adhesion layer that glued the nanostructures to a metal substrate.

Now researchers at Rice University have expanded the understanding of plasmonics beyond just the nanostructure itself and down into the metal substrate. They expect that their increased ability to characterize and manipulate the plasmonic effect could make plasmonic devices viable alternatives for highly complex optoelectronic devices like optomechnical oscillators, which couple photons into mechanical resonators and are used in photonic and wireless communications applications.

“At this moment, we are not trying to replace conventional optomechanical oscillators with plasmonic devices because the optomechanical oscillator requires extra high quality while the plasmonic structure we have currently only has a decent quality factor,” explained Wei-Shun Chang, a postdoctoral researcher at Rice, in an e-mail interview with IEEE Spectrum. “However, the advantage to use the plasmonic nanostructures is that it is an excellent antenna to efficiently couple the photons into the mechanical oscillator. This property can potentially simplify the design of the optomechanical oscillator.”

In research published in the journal Nature Communications, the Rice team was able to further this long-term aim by establishing a relationship between acoustic phonons and plasmons. Plasmons are the waves of electrons that move along the surface of a metal after it’s been struck by photons. And acoustic phonons are the vibrations of the metal itself after being hit by photons.

Both phonons and plasmons have distinct frequencies depending on the kind of light that has generated them. The Rice team found that they could make a direct connection between the resonant frequencies of phonons and plasmons by using pulsed laser light.

In their experiments, the Rice team aimed pulsed laser light at gold nanodisks causing them to vibrate. The vibration of the gold nanodisks—the phonons—could be tuned by changing the thickness of the material to which the gold nanodisks were attached.

“The plasmons of a gold nanodisk is a collective oscillation of conduction band electrons,” explained Chang. “Illuminating the nanodisks with short light pulse impulsively launches the acoustic phonon modes. The acoustic vibration of nanodisk arises from the absorbed photon energy by surface plasmon and then transferred to the lattice. More energetic phonons correspond to larger vibrations of atoms within the gold nanostructure.”

Chang believes that this work could pave the way for future plasmonic structures that are far simpler than today’s current optoelectronic devices.

“Plasmonic nanostructure can act as antenna and mechanical oscillator and don’t require complicated design,” he said. “It can be as simple as a disk as shown in the paper. Plus, the size of the plasmon structures can be down to nanometer scale to minimize the size of the device.”

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3D-Stacked CMOS Takes Moore’s Law to New Heights

When transistors can’t get any smaller, the only direction is up

10 min read
An image of stacked squares with yellow flat bars through them.
Emily Cooper

Perhaps the most far-reaching technological achievement over the last 50 years has been the steady march toward ever smaller transistors, fitting them more tightly together, and reducing their power consumption. And yet, ever since the two of us started our careers at Intel more than 20 years ago, we’ve been hearing the alarms that the descent into the infinitesimal was about to end. Yet year after year, brilliant new innovations continue to propel the semiconductor industry further.

Along this journey, we engineers had to change the transistor’s architecture as we continued to scale down area and power consumption while boosting performance. The “planar” transistor designs that took us through the last half of the 20th century gave way to 3D fin-shaped devices by the first half of the 2010s. Now, these too have an end date in sight, with a new gate-all-around (GAA) structure rolling into production soon. But we have to look even further ahead because our ability to scale down even this new transistor architecture, which we call RibbonFET, has its limits.

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